New York  - Negotiators held a "good discussion" Thursday on possible tough measures against North Korea for exploding a nuclear device and firing a string of missiles this week despite international protests, Japaneses UN ambassador Yukio Takasu said.

The closed-door discussion was held by the five UN Security Council permanent members - the United States, Russia, France, China and Britain - plus Japan and South Korea for at least the second time this week since Pyongyang conducted the nuclear test on Monday.

Takasu told reporters after the meeting: "It was agreed among the group that sensitive matters are now being handle in consultations and we agree that we should not, at this time, share them with the media."

"We are doing very good work. There has been a good understanding and cooperation among the group that the UN Security Council must respond clearly and strongly as soon as possible," Takasu said.

While avoiding speaking on behalf of China, he said that Beijing "understands the situation and is working very constructively" with the group.

Russian Ambassador to the UN Vitaly Churkin said that negotiators worked on "specific elements for the future resolution."

Churkin and Takasu declined to give more information on the discussion.

The activities of the five permanent members were being coordinated by US Ambassador Susan Rice, who met Thursday with UN Secretary General Ban Ki-moon to review the negotiations.

Japan in particular has called for new, tough measures against North Korea in addition to the set of comprehensive sanctions imposed on North Korea after it exploded its first nuclear bomb in 2006.

Those sanctions include an embargo on sales of weapons and nuclear technology to North Korea, a freeze of assets and resources owned by North Korea abroad and a ban on travel for certain regime officials.

In Washington, the US State Department announced Thursday that Deputy Secretary James Steinberg would visit Japan next week with the North Korean nuclear issue on the agenda. He was due to be there Monday-Wednesday for meetings with senior Japanese officials.

Steinberg will head to Tokyo after Friday-Sunday meetings in Singapore for the Shangri-La Dialogue on East Asian security trends. (dpa)